Concern for the environment as well as increasingly stringent regulation of air quality, pollution and hazardous waste has created a need for alternatives to the use of petroleum and petroleum-based products in ink compositions. The primary focus has been on the development of water- and soy-based printing inks. The major reason for using water-based ink compositions is that because organic solvents are not present except in very small quantities, potential problems such as toxicity, flammability and other hazards are minimized. The major drawback of the currently available water-based inks, however, is their generally poor water fastness, which limits their utility.
The present invention is addressed to the aforementioned limitation in the art, and provides a water-based ink composition which is also water-fast. That is, the ink compositions are prepared in water, substantially without toxic and/or hazardous organic solvents, but after printing and drying become insoluble in water and many of the common organic solvents as well.
The novel ink compositions are advantageous in other ways as well. In contrast to many ink compositions of the prior art, the compositions of the invention may be used on a wide variety of substrates, dry quickly after application, and tend not to bleed or smear after drying. In addition, the present ink compositions are generally low in viscosity (and thus relatively easy to work with), display good soak resistance, and have a relatively long shelf life, typically on the order of a year or more.
Traditional water-based inks are based on resin systems which are dispersed in water. Several references describe inks which are based on aqueous vehicles. U.S. Pat. No. 5,106,417 to Hauser et al., for example, describes low viscosity aqueous printing ink compositions based on polyacrylic resins containing carboxyl groups, and which also contain a humectant, pigment and, optionally, a water-dilutable organic solvent. U.S. Pat. No. 5,166,245 to Zuraw et al. describes water-based printing inks made with modified rosin grinding resins. U.S. Pat. No. 5,242,489 to Schwarz, Jr., et al., describes an ink composition containing a polymeric additive in addition to a colorant and an aqueous liquid vehicle. U.S. Pat. No. 5,244,496 to Easton et al. describes a water-fast ink composition containing an amine, an acrylic emulsion resin binder, a triamine dye, and water. However, the water-based inks disclosed in these references do not provide the aforementioned advantages of the invention; primarily, these inks of the prior art are not both water soluble and water-fast.